Imagine there was a material that was mostly identical to steel in almost every way, but instead of a density of $7.85–7.87 g/cm^3$ it would be a tenth of that. That is about 4 times lighter than aluminium is.

The idea is that all other properties such as

hardness/elasticity

brittleness

potential sharpness

are identical to those of the steel that was used for medieval weaponry anyway.

Chemical properties, as well as the forging process, are to be ignored as it is a fictional material.

Would using this material to craft swords and daggers be advantageous compared to creating them with traditional materials?

I am fairly certain that longswords would be pointless, as they partially rely on their mass to have an impact, but short swords, or even daggers, might be extremely useful as they would be very easy to use and hide. I am guessing the force of the hand/arm that drives the dagger into someone would suffice to tear the flesh.

Answers should elaborate on whether adaptions or changes to traditional weapon designs would be required to make the weapon profit from the unique material properties and offer advantages over the traditional weapons.

This question is part of a series regarding weapon and armour design using fictional materials with unique properties

This is the first question of the series. So there are no links to others yet.

$\begingroup$Aside from the effectiveness of weapons made from this material - I think early manpowered flight would happen with this material, eg gliders etc - leading to a different type of combat.$\endgroup$
– SeanRJul 5 '18 at 9:05

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$\begingroup$@ArtificialSoul Any longsword is a bad choice against someone in armour, swords were not anti-armour weapons. When forced to be used as such, they were halfsworded and the user tried to manoeuvre the point into a gap. (Which would of course be easier with a lighter sword.)$\endgroup$
– Grimm The OpinerJul 6 '18 at 12:33

12 Answers
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In weaponized combat, the use-case and fighting style will vary with each weapon's size, shape, maneuverability, weight etc. With the materials of choice for weapons being steel over the last couple thousand years, we developed combat style for short-and-maneuverable weapons as well as big-and-heavy weapons, but don't have many big-and-light weapons because materials sturdy enough to make weapons simply weigh too much.

In terms of fighting styles that focus on speed, such as knife fighting (a common example of weapon for this is a dagger) the fighter has a sturdy and maneuverable weapon but must sacrifice reach.

Longer swords, on the other hand, sacrifice speed in order to gain reach and the ability to deliver stronger blows (both because of their weight and their length) and granting them the ability to slash through target.

Some sword designs have tried to combine the two, the main one which comes to mind being the rapiers which are mainly intended as long-yet-agile thrust weapons, but they somewhat retain the ability to slash.

The existence of rapiers is proof enough for me that there is a good use-case for long, agile, thrusting swords; for such swords a metal such as described would certainly be very useful. The weight (and therefore agility) would be similar to that of the modern-day foil used for competitive fencing. Modern-day foils are very agile but lack the strength to be useful weapons (granted, that's by design, but you would not be able to make something strong enough at the same weight). A weapon as agile as the foil and as solid as the rapier would certainly be of interest.

As for long swords (such as the claymore) we've never seen a lighter equivalent, but that speaks more to the lack of viable materials for such a weapon than a lack of usefulness for it. Some people would certainly experiment with it, and I'm sure that we would see new combat styles develop for it. Just because they wouldn't work for current combat styles doesn't mean that no combat style could be developed for them. It could fill the gap between swords and pole arms.

Personally I think that small knives (blade <10 inches) would be the least beneficent of this new material since they are already quite maneuverable, limited mostly by their shape and size than their weight. Short swords and rapiers which are already "hybrids" between quick and long would improve by large margins.

Lastly, I'll discuss the required differences construction that would be required for knives. The balance of a good knife is somewhere around the guard, the point at which the handle stops and the blade starts. If you were to drastically lighten the blade material (to 0.78 g/cm^3, a tenth that of steel, nearly identical to that of oak) and keep the handle materials the same, you would end up with a knife that is very butt-heavy. You would need to thin out the handle or use lighter materials on it, or both.

$\begingroup$Wish I could upvote this again. Most people assume medieval sword combat was just hacking at each other's armour until one died. HEMA and Talhoffer style fighting tell a contrasting tale!$\endgroup$
– KorthalionJul 5 '18 at 8:26

$\begingroup$Note that while a claymore might be a long sword, it is not a longsword.$\endgroup$
– Grimm The OpinerJul 6 '18 at 12:28

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$\begingroup$@Alexandre Aubrey I am not criticizing your answer which is obviously fantastic. I was just pointing out one fact which is often misunderstood because of popular media. For example movies like to give rapiers to women because they are "lighter", but we know in reality that they are not so this is a popular misconception. I was just highlighting this fact for what it is worth. Possibly not a lot..$\endgroup$
– Tyler S. LoeperJul 6 '18 at 15:58

Such a metal would be good for thrusting weapons like a daggers, shivs, and rapiers; mediocre for slashing weapons like cutlasses, scimitars, katana, etc. that rely more on their weight but still use speed and a cutting edge for most of the damage; but poor for a throwing knife (poor balance, affected by wind) or any edged blunt-force weapon (like a long sword, most swords fall into this category). It would be worthless for maces, flails, or any other non-edged but metal blunt-force weapons.

On the other hand, such a metal would be wonderful for bayonets, arrow tips, spear tips, or any other application where the blade is connected to something else that represents the bulk of the mass. It would make balancing such an object much simpler and would overcome the problem of breaking under the leverage applied by the item the blade was mounted to.

Ultimately, the metal would be fabulous for door bracing, carriages, or any other construction where metal is used to support the construction but the weight is an issue. The guys using wheelbarrows and building skyscrapers will erect a statue in your honor.

$\begingroup$Comments are not for extended discussion; this conversation about objections to this answer has been moved to chat.$\endgroup$
– Monica Cellio♦Jul 6 '18 at 1:28

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$\begingroup$Please note, that swords were not "blunt-force weapons". Contrary to popular myths, swords were very nimble weapons, their center of mass is very close to the handle, so they would be very bad at bashing even unarmored opponents, let alone armored ones. Swords are for cutting and stabbing, not for chopping like with an axe. Here is a useful video demonstrating the difference between a sword and a mace: youtu.be/fg-GhnAO1VE?t=423. No sword could cut through metal armor, especially full plate, so there was no point in making swords heavy and dull to bash armor, it would be useless.$\endgroup$
– vszJul 6 '18 at 19:09

As others have said, your ultralight steel will be best for thrusting weapons, but I think there are more uses people are forgetting.

You could have polearms of extraordinary strength. Normal polearms have hafts made of wood, but yours could have hafts at least partially made of this new steel. This would let you swing longer warhammers or halberds than usual.

If the new steel can be combined with traditional steel, it would be useful for swords as well. You could have a sword with traditional steel in/near the hilt and new, light steel towards the tip. This would let you have a much longer sword without sacrificing its balance.

One big disadvantage however, is that this new steel will have less inertia. When you parry with a traditional steel sword, a lot of the energy of your foe's swing will be wasted pushing your sword. With lighter steel, your sword will waste less of your foe's energy, and you will feel the impact a lot more in your hands, wrists, and arms. You will thus be at more risk of having your sword knocked out of your hands. You have similar problems with armor made of light steel. Being struck by a blunt weapon while wearing armor made of light steel will be more dangerous than in armor made of traditional steel because the light steel has less inertia. It absorbs less of the force, and so more of it goes into hurting you.

$\begingroup$I like the combination idea of regular steel and light-weight steel. It wouldn't make a significant difference in regular wielding, but increasing reach is always a strategic advantage.$\endgroup$
– ArtificialSoulJul 4 '18 at 17:03

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$\begingroup$Can confirm, having wielded a full-weight steel bill on the battlefield multiple times, having a lighter head would make you at least twice as deadly!$\endgroup$
– KorthalionJul 5 '18 at 8:21

Most of your weaponry would be near useless. Such light weight steel would enable MUCH thicker armor with out the massive (heh!) weight penalty. So now your weapons - which will depend on speed and sharpness for damage vs being a slightly sharp club - will have an even harder time doing damage through a double layer of chain mail, or plate, etc.

I would predict that many actual weapons will still be made from traditional steel - they need the weight. Armor, wagon wheels, ships, etc could be made from the new light weight stuff....

$\begingroup$Your weapons will also be much much longer, and so their tips will be moving much faster, meaning they will hit much harder. I suspect this will cancel out the added armor thickness, leaving the balance between armor and weaponry unchanged.$\endgroup$
– Ryan_LJul 5 '18 at 4:15

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$\begingroup$Good point about the armor but as far as I’m aware it’s always been pretty hard to stab straight through plate mail. Blunt weapons and weapons like daggers (to hit small vulnerable spots) were mostly used.$\endgroup$
– MichaelJul 5 '18 at 5:20

Steel has a density of about $8,000kg/m^3$, which meas ubersteel has a density of about 800kg/m3 which makes it heavier than wood unless somebody is making magically dense wood (which might make a good competitor to metal) woods. (Thank you Alexandre Aubrey for pointing me to the wood-density table; thanks to Loong for pointing out a math error.) This could be used to strengthen a traditional quarterstaff.

The advantage of ubersteel over wood is the strength it would bring. The disadvantage is that it would probably be much more expensive to have one made in metal than having one made in wood with only some iron added to the ends which makes it stronger where it hits things and also adds mass where it needs it the most. I think the increase in strength and durability is more important than the mass, but I've never had the opportunity to use a iron-shod staff.

A lot of uses for it depend on the cost. If it's expensive, it will not be used in melee weapons at all.

However, think about it's uses in siege weaponry. Even if it were to only partially replace or reinforce the wooden parts, a catapult (and like devices such as the trebuchet) could be made to be easier to move which means faster aiming, stronger, which means more distance or higher payloads, and if done right, faster to construct.

It would also be used in buildings and vehicles, even if those vehicles are just carts.

Shipwrights would love this stuff! To be able to have steel-like strength without the problems.

I don't now if you are considering canons, but being made of this material would really please your admirals and even cavalry. Lightweight artillery is very important in ships and when you have to haul your cannon around with horses. Being lighter weight, they would be more easily taken through muddy fields and other problematic terrain. Remember that most weapons spend more time being transported than being fired.

I'm not sure much would be left for the common man. To be honest, the best use in weapons are stabbing weapons like a dagger, arrowheads (and yes, arrows can fly perfectly well with a light head), and spearheads.

In the medieval times, there was very little metal that we would call steel. The technology of the times used bloomery furnaces which required a lot of work to produce steel good enough for a sword. This is one of the reasons that most people didn't use swords, despite all the books and movies to the contrary.

$\begingroup$Why do you think that a light quarterstaff is better than a heavy?$\endgroup$
– pipeJul 5 '18 at 8:09

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$\begingroup$@pipe i think the idea is to have a steel quarterstaff instead of a wooden one. you could combine regular steel and light-weight steel to achieve the same weight and balance, but it would be significantly sturdier$\endgroup$
– ArtificialSoulJul 5 '18 at 8:33

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$\begingroup$Yes. I use an aluminum quarterstaff to practice by myself. It's heavier than any wooden staff I have. As for weight, a quarterstaff is mostly a weapon that works by speed, with some damage depending on mass.$\endgroup$
– NomadMakerJul 5 '18 at 14:48

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$\begingroup$If nothing else, you could cap both ends of the staff with the ubersteel, making them do more damage but without too much of a weight increase$\endgroup$
– KorthalionJul 6 '18 at 10:52

$\begingroup$Good answer. As for the first sentence (of this new material being lighter than wood): density of 0.78g/cm^3 is about the same as some of the denser woods, but denser than most. That doesn't invalidate anything you said, it makes some of them even more relevant if you compare it to the woods used for the construction of some of the items you mention. I'd recommend looking at this list to compare densities of different woods (and maybe link it in your answer to give more credibility to the claim)$\endgroup$
– Alexandre AubreyJul 6 '18 at 19:55

I'd say that you're probably right that daggers and shortswords would benefit from this material whereas axes, warhammers, maces and arrows would probably be better with heavier steel as they rely at least in part on the mass behind them.

Rapiers and other thrusting swords (like late medieval swords) would probably benefit, whereas hacking swords like scandinavian/viking swords and falcatas would probably be better in steel. Draw-cut swords might be better in a lighter material too as they rely less on weight to strike.

Spears would also benefit (if not thrown) because you could get better balance without the heavy spearhead. Or rather, you'd wouldn't need as heavy a counterweight on the back of the spear to balance the head, allowing you to move it around faster (lower polar moment of inertia).

Longswords would be an interesting case. Yes they rely somewhat on mass, but with a much lighter material you could probably make a verylongsword quite wieldy which is able to outreach an opponent, with techniques using more thrusts and draw-cuts. Not sure how it would affect parries and winding though.

Poleaxes would be interesting too, or any weapon that relies on leverage to improve its strike (like falxes). I'm not sure how that would play out. Yes you have less mass to accelerate, but as anyone who's seen a quarterstaff in action knows it's perfectly possible to get a nasty amount of force behind a strike from the haft alone.

$\begingroup$The spears, longswords and poleaxes you proposed are pretty interesting. I didn't think about using the light-weight material to increase the weapon size to still have roughly the same moment of inertia properties and thus increasing reach by a long shot.$\endgroup$
– ArtificialSoulJul 4 '18 at 16:58

$\begingroup$Wikipedia says a Claymore weighs 2.2–2.8 kg (4.9–6.2 lb) with a total length of 120–140 cm (47–55 in). I suspect a 1/4 weight version would be used more like a rapier simply because that's where the weight and length end up$\endgroup$
– JollyJokerJul 5 '18 at 7:15

$\begingroup$@JollyJoker Agreed. There's another weapon I was thinking it might end up like, which is sort of like a longsword, but not bladed and triangular in cross section with a very fine point. Damned if I can remember the name of it though. Knights used it as a cross between a longsword and a lance. That'd work well too and probably be close to what we're looking at.$\endgroup$
– YnneadwraithJul 5 '18 at 8:20

$\begingroup$@JollyJoker It's an estoc that I was after!$\endgroup$
– YnneadwraithJul 5 '18 at 8:46

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$\begingroup$@Ynneadwraith Assuming cost is not a problem, thrusting weapons like the estoc made completely from metal would presumably be superior to spears and such with wooden shafts.$\endgroup$
– JollyJokerJul 5 '18 at 10:20

You're right that it's actually a disadvantage to have slashing swords or crushing weapons like maces be light weight, they do less damage because they have less energy on impact.

However for stabbing weapons like stiletto or misericorde daggers or even for long swords like the rapier light weight but physically tough and/or springy material is a serious advantage since the weapon can be moved faster and control more easily.

I would expect that there would be problems with this material for weapons not because of the weapons but because Armour is now 10 times as effective as it was at a given weight, weight has always been the limiting factor for metal armours.

I think one thing people are not thinking about with regard to cutting weapons is that the sword could just be made thicker. Also using F=MA and P=MV we can see that as long as the user is swinging his sword faster he can make up for a lot of the weight difference.

If this super steel is 1/10 as dense then presumably it has 1/10 the contents therefore there would be 10 times the mass of this new steel compared to regular steel. This means we would probably see much wider more extremely tapered swords to add the mass.

However swords would almost definitely not be used in this universe as the second armour was invented it would require 1/10 the amount of ores to make the steel and so using 1 mine that could mine 10 suits before you would now get 100 suits.

A huge draw back of mail and other armours was the difficulty to make however more of the population would be professions who used steel as countries would have far fewer men working in the steel mines.

In pure attack, I'd argue that nearly all swords rely more on sharpness and speed for damage than mass. That is why the point-of-balance is close to the hand compared to impact weapons like axes and maces. (Not that we shouldn't over-emphasize the importance of point-of-balance, but I believe it is relevant here.) This is also why, against heavy armor, the "murder stroke" was sometimes employed, where the wielder grabbed the sword by the blade and used it more like a warhammer than like a sword.

But they rely on mass in the bind. This is not only when blocking or deflecting enemy strikes but also when controlling your opponent's weapon during an attack. This is why rapiers generally weren't much lighter than longswords.

Opponents with otherwise identical weapons but one being conventional steel and the other being your lighter density steel, I believe the conventional steel wielder would have a significant advantage in controlling their opponent's sword. The wielder of the low density sword would need to exploit quicker disengages, but I'm not sure doing so would make up for the disadvantage.

I am less sure on how this low-density steel could be exploited in weapon design.

I'm going to disagree with the idea that this would be a bad material for a sword, with the prevalent idea that it reduces the force of the swing. The force of a slash is determined by more than just the weight of the weapon, it's also determined by the speed. In fact, it's determined more by speed than by weight.

Newton's second law of motion states that F = ma, also written as $F = \frac{1}{2}mv².$

Since we are not changing gravitational constants, anything we do to the weight will have the same factor of change to it's mass.

If we reduce the mass of a sword by a factor of ten, and keep speed or acceleration the same, then yes, the force is also reduced by a factor of ten. However, a human using a much lighter blade is going to be able to move that sword much faster than the heavier one. If we make an oversimplified assumption that if we reduce the weight by 10x, then we can increase the speed it is moving by 10x.

So, this says we've increased the force of the blade by 10x by reducing the weight 10x.

If we only triple the speed at which we swing the sword, we can see that we have almost the same force of impact:
$F = (1/2)(m/10)(3*v)² $
$F = (1/2)(m/10)9v² $
$F = (1/2)(9/10)mv² $
$F = (9/(2*10))mv² $
$F = (9/20)mv² $
$F = 0.45mv² $

Now consider that if a soldier trains with a regular steel sword, then uses the lighter version in battle, they will have just as much muscle mass as the soldiers with the heavier sword. The lighter sword will be so much easier to swing that they will get a much faster slash than with a heavier sword. This adds the ability to change the angle of attack faster as well as simply attacking faster, and attacking for longer stretches of time.

A lighter sword to carry over their forced marches would make them less exhausted or able to travel farther. I carried an M16A2 during marches in Army Basic Training, and at 8.8 lbs, it gets really heavy quite quickly.

JollyJoker, in a comment on another answer, says that a claymore weighs around 5.5 lbs. A katana weighs around 2.5lbs, even made from steel. I think you would find fighting styles closer to a katana with the 10x lighter swords. You might also find fighting styles closer to kung-fu, which also uses lighter swords.

Another answer suggests fighting styles along the lines of an epee/foil/rapier, but if the enemy is using armor, that's not likely to work. You would have to find the joints of the armor to attack, and that's pretty hard when the armor is constantly moving. Unless the soldier is an expert fencer, they would basically have to be lucky or wear their opponent down in order to dispatch them.

A TV show I saw a while ago (BBC or a Nat. Geo.), showed that a katana is actually better at attacking armor than a traditional English sword. They did actual tests with actual armor and swords.

The long sword put a decent dent in the armor, but the katana cut into it. Unfortunately, the person doing the tests wasn't really trained in either style of sword, and I don't think the swords they used were of good quality, but you get the idea. (A trained samurai would aim to use a spot about 1/3rd to 1/4 of the length of the blade from the tip, not the center of the blade, like in the video.)

$\begingroup$This answer appears to assume a human arm can actually swing anything 3-10x as fast as a traditional sword, which may not actually be the case. I'd like to see some source that shows a human arm can actually move that fast (because I'm pretty sure a person's arm can go maybe twice as fast tops with no load compared to swinging a standard sword). That's where the idea that you lose power with a lighter blade comes from - you can mathematically regain that force by increasing speed to compensate... but you can't physically gain that speed.$\endgroup$
– DeliothJul 5 '18 at 21:42

$\begingroup$@Delioth i agree. There are certainly martial arts that rely on extremely fast punches (e.g. Wing Tsun Kung Fu) but those punches are not comparable to the moves you make while swinging a sword. And they are not even 10 times as fast as a regular swing.$\endgroup$
– ArtificialSoulJul 6 '18 at 6:21

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$\begingroup$"$F=ma$" here $F$ is a force. But then you write "$F = \frac{1}{2}mv²$", where the right side is kinetic energy, so why are you reusing $F$ which is normally used to denote forces and not $E$ which is normally used for energy? This inconsistent use of variables makes your post pretty confusing.$\endgroup$
– CodesInChaosJul 6 '18 at 9:16

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$\begingroup$Doing a little bit of research, some sources give me the record swinging a baseball bat (which is just under 2 pounds) at around 80 mph. Fastest sword swings clock at around 43 mph, though that may be at a different point on the lever compared to a bat. Either way, the fastest punch (and thus the fastest your arm can physically move) ever recorded was at 45 miles per hour... so we aren't getting anything close to triple the speed, even if our sword is perfectly weightless. @ArtificialSoul these blades are going to be less effective than a normal steel sword (at least for striking power)$\endgroup$
– DeliothJul 6 '18 at 14:56

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$\begingroup$Well... a punch is a straight line. The bat swing was measured at roughly the tip of the bat as far as I could tell. It's to get some context - if you can swing a 2 pound baseball bat at 80 mph, that's really close to the fastest you can swing any object regardless of weight. In any case, outside of the largest blades you aren't going to be able to move your arm fast enough to get extra energy into the strike - it'll be going a little faster but the reduced mass means it won't have nearly the same amount of energy.$\endgroup$
– DeliothJul 6 '18 at 15:51

Everybody seems to be missing the biggest weapon -- commerce! (And logistics). This material is going to be an incredibly useful building material for both ground and water based travel (and when the time comes air).

The size of ships, boats and wheels this will make possible...a ship made out of wood has a maximium length of about 300 feet one made out of steel thousands of feet. For internal roads, imagine the loads you could haul with 10 foot diameter wheels!

Armies are going to be larger and faster than in or world, able to cover more and more varied ground.

As for its use as pointed weapon, its going to be so effective as armor, that making swords out of it would be a waste of time.

$\begingroup$Your answer is indeed correct, but it does not answer the question. The question specifically states application in swords and daggers (mainly to avoid being too broad) and your answer does not even mention that. It is not a bad answer, so i won't downvote it, but please make remarks like this in the comments to the question in the future. (Some people already did, by the way.)$\endgroup$
– ArtificialSoulJul 8 '18 at 13:05

For what it's worth this is not necessarily a fictional material. I obtained a section of a helicopter blade once (my sister was a PA for a exec at Hughes) The interior of the airfoil was filled with foamed aluminum. No idea how they made it.

A multiphase material might well be as strong as steel and a fraction of the weight.

Look at graphite composite bike frames. Far stiffer than steel, but at 1/10 the weight. I can buy a kevlar canoe that is 1/4 the weight of a traditional oak rib, cedar plank, painted canvas canoe and it will take a lot more punishment. (But not as pretty...)

I saw a 3d printed copper cube. Overall structure was tetrahedral internally. Despite being made of pure copper, it was a heat insulator better than most common insulators. -- copper only took up 3% of the volume, and the nature of the connections was such that the path length was several cm per cm thickness. It was still strong enough to stand on.

Consider a sword made with a foamed metal core for stiffness, and a tungsten carbide skin for carving the other guy's armour. Or a sapphire lattice sword, with the lattice arranged so that it would have a certain spring. Put a directional anti-reflection coating on it so that it is visible from the hilt end, but hard to see from the pointed end

$\begingroup$While the end result is indeed similar and the applications correct, this is not what the question is about. It is about how to modify swords using such a material - and it also states it is a medieval scenario. I am guessing real foamed metal is not something a blacksmith could craft - hence the need for a fictional material.$\endgroup$
– ArtificialSoulJul 12 '18 at 10:20